This invention relates to an improved safety latch construction for use with doors, windows, or any other structure which needs to have the safety feature that permits partial opening without losing the protection of the latch.
The commercially common form of such safety latches is the chain-and-slot construction customarily used on hotel room doors. Because of the deficiencies of those latches, the patent art discloses numerous structures, many of them during the 19th Century, intended to substitute a rigid, pivoted latch member for the chain structure. As pointed out in one of those prior art patents, U.S. Pat. No. 4,408,789, the safety "chains provided are usually not sufficiently strong to withstand a heavy impact on the door and, therefore, do not provide the desired safety from forced entry by intruders." That patent also lists a number of prior art efforts to solve the safety latch problem. Additional deficiencies of chain latches are discussed in U.S. Pat. No. 3,458,226 which refers to (a) their susceptibility to unlatching if slightly ajar, (b) their unsightly appearance, and (c) their inconvenience.
The long-standing existence of this problem is further emphasized by several very old prior art patents which were discovered by the present applicant in searching this field of art, including the following U.S. Pat. Nos. 189,822, issued in 1877; 251,732, issued in 1882; 465,185 issued in 1891; 473,785, issued in 1892; and 534,716, issued in 1895.
Because there has been an exhaustive search for a solution to this problem, the continued use of the unsatisfactory chain latches indicates a need for the present invention.